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Witnesses.

(No Model.) 2 Sheets-Sheet 1.

F. A. PIGKERNELL & F. W. DUNBAR. TELEPHONE AND SIGNALING OIRGUIT.

No. 494,385. Patented Mar. 28 1893.

(No Model.) '2 Sheets-Sheet 2.

F. A. PIOKERNELL & P. W. DUNBAR.

I TELEPHONE AND SIGNALING CIRCUIT.

No. 494,385. Patented Mar. 28, 1893.

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THE NORRIS Pzrzns co, Pnofauvna, wAsHiNm'uu. n cdisconnecting thestation trunk from the local- UNITED STATES PATENT CEFICE.

FRANK A. PIOKERNELL, OF NEWARK, NEW JERSEY, AND FRANCIs W.

DUNBAR, OE NEW YORK, N. Y., ASSIGNORS TO THE AMERICAN TELE- PHONE ANDTELEGRAPH COMPANY, OF NEW YORK.

TELEPHONE AND SIGNALING CIRCUIT.

SPECIFICATION forming part of Letters Patent No. 494,385, dated March28, 1893,

Application filed December 15, 1892. Serial No. 455,297. (No model.)

T0 at whom it may concern.-

Be it known that we, FRANK A. PIOKER- NELL, residing at Newark, in thecounty of Essex and State of New Jersey, and FRANCIS W. DUNBAR, residingat New York, in the county and State of New York, have invented certainImprovements in Telephone and Signaling Circuits, of which the folowlingis a specification.

This invention relates to transfer systems and theirsignalingapparatusintelephone central stations. Its objects generally stated, aretofacilitatethework oftransferringtelephonic connections between localand toll line switchboards; to avoid the inconvenience in operationarising from the massing of switchcords; to provide a system ofreciprocal signaling between the said local and toll boards; and toinsure that when a repeating induction coil has been interposed in thecircuit of the station trunk, forming the connection between the 10- caland toll line boards (an arrangement frequently adopted in theinterconnection of double and'single conductorcircuits) itcanbeautomatically disconnected therefrom by the act of telephone circuit. Itis to be premised that in large telephone exchanges there are both localand toll lines. The local lines converge from substations to the centralstation and connect usually with a multiple switchboard, having a numberof independent operators sections. The toll lines areinterstation trunkswhich extend between independent exchanges, and at each central stationterminate in independent switchboards. Station trunks therefore arerequired in each central station,

to serve as intermediary conductors between the multiple and toll lineboards; and since it would be cumbrous to branch or loop these to allsections of the multiple board, it is customary to terminate them at onesection only (usually the end section) and when acall from anysubstation comes in foratoll line connection at its regular section, tohave the operator there, communicate over an instruction circuit withthe end section operatorinstructing the latter to make the required tollboard connection. It is also usual to establish and make use of suchinstruction circuits between the end section and other operators, aswell as between the said end section operator and the toll boardoperator.

The different features of this invention are most highly advantageouswhen operated in association with a large exchange and a multipleswitchboard; but are equally applicable to smaller exchanges andordinary or single section switchboards, and in this specification it isto be understood that the term local switchboard includes either amultiple switchboard whose toll business is operated from its endsection, or a single switchboard of any preferred construction.

Heretofore, office trunks have been provided at both ends withspringjack or socket terminals, and this characteristic has necessitatedtwo plugs and a cord conductor depending from both, for each connectionbetween the said trunk jacks and the jacks of subscribers lines. Inconsequence of this, the massing and tangling of cords becomes veryobjectionable; but retaining the same system, the only remedy for thetrouble is to largely increase the amount of switchboard apparatus, andthe use of complex springjacks. Employing the organization described inthis specification, it becomes possible to terminate the station trunkin a cord and plug, instead of a springjack as heretofore, and toestablish a connection with any local substation circuit by insertingthe said terminal plug into the socket of such substation circuitdirectly. The number of cords is thereby at once halved, while but onemotion also is then necessary. 5

Heretofore it has been requisite to'transunit an order over theinstruction circuit, not only for connections between toll and' localcircuits, but also for disconnections; which thus involves twocommunications over the said instruction circuit for each connection. Byemploying the organizations described herein, it is only necessary touse the instruction circuit once, viz: in ordering the establishment ofa connection; since the disconnection of the station trunk at the tollboard end thereof, is enabled automatically to operate a signal at thelocal board indicating that disconnection is desired, whereby the workof the instruction circuit is largely reduced, and time saved.

In the station trunks between the toll and local switchboards, it isrequisite to provide means for including a repeating induction coil tobe used in the interconnection of a double with a single line circuit,or whenever either the toll or local line is noisy. The mode heretoforeemployed, has been to have two terminal office trunk springjacks withthe repeating coil connected between them, to be introduced or not,according to the springjack employed; or else to control the connectionof the said coil by a switch, which in one position acts to introducethe coil,and in the other maintains the disconnection thereof; thesearrangements however involve on the one hand a multiplicity ofappliances, and on the other the liability owing to neglect, of thecontinued presence of the coil, (which of itself is disadvantageous)even when not required. In the invention herein described, the repeatingcoil is introduced when required, by a positive operation; but isautomatically withdrawn from the circuit by the act of disconnecting theoflice trunk, and the consequent termination of the communication withwhich the said repeating coil has been concerned.

111 the accompanying drawings which form a part of this specification,Figure 1 is a diagram of a portion of both toll and local boardconnecting apparatus, and their circuits, together with the stationtrunk and its associated signaling and other appliances. Fig. 2 is adiagram of the signaling circuit and apparatus of the said office trunk;and Fig. 3 is a detail illustrating the mechanism whereby isaccomplished the automatic withdrawal of the repeating coil.

In Fig. 1, the organization is shown as having two general divisions,that marked M on the left of the central broken line, comprising thedevices all ordinarily placed at the section of the multipleswitchboard; and that marked T on the right of the said line beingordinarily placed at the toll switchboard. This figure shows severaldistinct circuits which to a certain extent are practically independentof each other. The circuit L is a local substation circuit representedon the section M as well as on the other sections (not shown) of thelocal switchboard, its wires 2 and 3 leading from the substation andfrom the next assumed section in one direction, and its wires 4 and 5leading from the next assumed section in the opposite direction. Thecircuit X is merely a loop to a busy signal current generator or likedevice. The circuit L is the office trunk between the local switchboardM and the toll board T, and has two conductors 8 and 9. This circuit atM is adapted for connection with any local telephone circuit, and at Twith any inter-office trunk or toll line.

L is the terminal loop of a toll line or interoffice trunk, extending bywires 10 and 12 to a distant station.

L is an instruction circuit leading from contact terminals at the tollboard to the operators telephone at the local board.

L is a conductor leading from other local switchboards to the operatorstelephone at the board M with which it is inductively connected.

D is an independent associated signaling circuit extending between thelocal board M and the toll board T, and provided with shunt circuits andappliances to be hereinafter described.

J is a plugsocket or springjack belonging to circuit L, whose conductors2 and 3 respectively have spring terminals (Z d therein, provided withresting contacts f f respectively, which may be connected withcontinuation wires 4 and 5 leading to other switchboard sections.

J is a special springjack wherein the terminal plug of the office trunkcan be placed it it be desired to indicate at the toll board that alocal line called for, is busy; its circuit X which is a closed loopconnects its spring contact m, and its frame or socket contact 0?, witha magneto or other generator m and thus operates a suitable annunciatorat the said toll board.

P is a loop plug which has tip, and sleeve or stem conducting surfaces19 and p insulated from one another, forming respectively the terminalsof the two conductors of the office trunk circuit L It is adapted to beinserted in the jacks J or J and the tip 19 makes contact with the innerspring (I of the former, and the sole spring 171 of the latter, whilethe stem 19 makes contact with the longer spring (Z of the former, andthe frame piece a of the latter. cuit L ending in the said loop plug isclosed through the circuits L or X having terminals in the said jacks.The plug P has no electrical relation with the signaling circuit D, butit has when in its resting socket, a mechanical relation thereto,maintaining the same discontinuous when in place, and permitting thesame to become continuous or to close, when taken from its restingsocket, for any purpose, by means of appliances shortly to be described.

The main conductors of the oi'lice trunk are represent-ed between thekey and the plug P by conductors 16 and 17 which in practice arecomprised in a flexible cord W (see Fig. 3) of sufiicient length toallow the plug to be inserted in any desired springjack, and which in amanner well understood, is provided with some form of automaticretractor, such as a Weight suspended in the bight of the cord.

0 is a repeating induction cord with two helices c and c and is arrangedto be interposed in the oflice trunk circuit, so that the terminal plugat the local switchboard end In either case the cirthereof, may have aninductive connection only, with the springjack at the other end thereof,during communications in which the jack J represents an earth completedinstead of a metallic circuit, or in certain other circumstances wherethe lines being noisy, it

becomes desirable to divide the telephone or in instruction or ordercircuits, which are normally incomplete. It is connected in the ordercircuit L extending from the toll board T, where it terminates incontact plates 1' 'r', to which the ends of the operators telephonecircuit may be applied, if it be desired to send an order. The plates 0"are of the form shown, in order that the twin plugs P P may readily andwithout care make contact with them for the purpose of closing thecircuit and connecting the operators telephone at T therewith. It mayalso be connected with a second order circuit L extending by wires 15from other sections of the local board M, at any of which the operatorstelephones E can connect therewith by means of keys K or otherwise asdesired. The connection of the circuit L is shown as being efiectedthrough the intermediation of an induction coil C one helix thereof 0being in closed circuit with the telephone t while the other 0 is placedin the order circuit 15, which is grounded at G R is a relay havingWound over its iron core two helices of wire, H and H It has a metallicframe piece q to which is hung in such a Way as to insure a goodelectrical connection, the spring armature g having a movable contactpoint g arranged upon the attraction of the armature, to make contactwith a front stop, which also I have called g so that when the saidcontact is-made, it may be described by that reference letter. The frontend of the relay core is bent upward and over the spools in the form ofa polepiece q, for the more efficient attraction of the armature. Thecoil H of the relay has a relatively large number of convolutions, and arelatively high resistance, one hundred ohms or thereabout. The coil Hof the relay has a relatively small number of convolutions and arelatively low resistance; ten ohms having been found satisfactory. Whenthe relay core becomes sufficiently magnetized, its armature isattracted and closes the contact g which normally is open. Once havingbeen closed however, the-armature will stay attracted with a much lowerdegree of magnetizing power than is necessary to first attract it, andmake the contact.

S is a self setting or restoring annunciator of any desired form, suchas a polarized needle, or a neutral magnet lifting its shutter into Viewwhen energized, and causing or permitting the same to disappear whendemagnetized. The construction and resistance of its winding should besubstantially equal to that of the low resistance relay coil H that isto say it'has relatively few convolutions, and offers a resistance ofabout ten ohms. It is placed directly in the main conductor portion ofthe signal circuit D. A signal circuit battery B, has one pole groundedat G and the other connected by the wire 24 with the relay frame g. Itis not essential, albeit convenient, that the relay and battery shall beplaced at the local board M; they may be 10- eated wherever desired,provided that the connections are arranged in the manner to bedescribed.

Referring to Fig. 3 it will be seen that the plug P when not in use hasits non-conducting handle h, resting in a seat S prepared for it in thetable or keyboard Q, and is closely associated with the push key whichcontrols the connection of the repeating coil 0.

The tip conductor 16 of the plug leads to the g inner spring a; of thekey, and the stem conductor 17 thereof, leads to the contact point 202on the tubular sheath thereof, through which the key spindle works. Theconductor 9 of circuit L of which conductor 16 is the continuation, endsin the fixed contact u on the other side of said tubular sheath,and theconductor 8 of circuit L ends in the inner contact spring 00 When thekey is undepressed, the said inner springs m and 50 rest on the saidfixed contact points u and a respectively, and the circuit L of theoffice trunk extends conductively to the tip and stem conductors of theplug P.

A branch including the wires 21 and 18, and the helix 0 of the repeatingcoil, extends from any point 12 on conductor 17, to the outer contactspring to of the key, where as long as 1 the said key is undepressed, itremains discontinuous. A similar branch including the Wires 19 and 20and the helix 0 extends from any point 12 on conductor 9 of circuit L,.to the outer contact spring w When the key .is depressed, its springsor and at? break contact with the fixed points it and u and make contactwith the outer springs to and w and when the said key is again elevated,the re-' verse is the case. When the key therefore is depressed, therepeating coil is included in the circuit L from the tip and stem of theplug P, which circuit considered as a whole then is no longer completeconductively, but inductively through the said coil 0.

To render the subsequent elevation of the key 10 independentof theaction or volition of the operator, the apparatus now to be describedhas been devised. The shank of thekey k is encircled by the spring gwhich has a hole through it for that purpose, and which is attached atits lower end to the frame of the key. The said shank has a squareshoulder 8 The spring g tends by its own resiliency to move in thedirection of the plug P, and when the key is depressed, does move, andengages the shoulder s as soon as the shank in its downward progresspasses through the hole in the spring. Normally the said spring isprevented from moving by the spring 9 which in virtue of the presence ofthe plug handle it in its seat S in the table Q presses it backwardly.But when the plug P is removed from its seat for insertion in a jack,the spring g is relaxed, and allows the spring 9 also to move, and toengage the shoulder of the key when depressed, thus providing aretaining device therefor. It is only when the plug P is withdrawn fromits seat and inserted in a local jack, that occasion arises for the useof the key is; consequently when it is necessary to interpose therepeating coil into the conversation circuit, the key may be depressed,and will remain so during the pendency of the connection because itscollar is engaged by the spring g Under these conditions the contactsbelow having been altered as described, the repeating coil is incircuit; when on the conclusion of the conversation the plug is removedfrom the local board jack, and restored to its seat, its shank willforce the spring g, and thereby the spring g outwardly, freeing the keyspindle therefrom and permitting it to rise under the influence of thespiral spring 5 This operation automatically disconnects the repeatingcoil from the conversation circuit, its presence there being no longerdesirable.

' Inasmuch as it is always necessary to withdraw the plug from the jackand restore it to its resting place on the completion of a com- 1nunication, it follows that the repeating coil cannot be left in circuitfrom the neglect or heedlessness of an operator.

At the toll board T are the springjacks J and J of the two conductors ofthe ofiice trunk; the two spring jacks J and J of each of any number oftoll lines or inter-oflice trunks; (one pair only for clearness beingshown) and a series of link connections (one only being shown) havingplug terminals P and P with a listening key K, ringing keys 76, and anda disconnecting annunciator e bridged between the two conductors of thelink as usual; and also the usual transmitting and receiving telephone Eand t, the former being in the local circuit 25 of a transmitter batteryI) and connected with the telephone loop through an induction coil 1';the jacks and plugs at the toll board end of the office trunk are in thepresent instance shown as twinjacks and plugs, that being a form ofmetallic circuit connection alternative to the well known single loopjack and plug. The several circuit arrangements of each link connectionare as usual, the member p of plug P being united by the cord conductors26 and 28 and the two ringing key normal contacts with the member of theplug P while the member 9 of the plug P is united similarly with themember 19 of P B is the loop from a call generator (not shown) and hasbranches 30, 31, to ringing key k and 33, 34: to key 70. The depressionof either key acts to send a call current out through its own twin plug,cutting oil? the other at the contacts u.

The disconnecting drop e is permanently bridged between the linkconductors 37 and 38 by the wires 39 and 40 and their extensions 41 and42; and the telephones are connected in the bridge when desired, by thedepression of the cam key K which presses the inner spring contacts :2as which are the terminals of the telephone loop against the contacts 10and w of the outer springs which are branch terminals of the bridgeconnection.

A is a signal annunciator of any ordinary type, and of a resistanceapproximately equal to that of the high resistance relay coil, say onehundred ohms. It is connected in the signal circuit D.

The springjacks J and J each have two other contact springsin additionto the springs s of their main circuit, which may normally or when aplug is not inserted, rest upon the insulated contact pins z which arelooped by the conductor 43 to the ordinary annunciator a. Thisannunciator is provided for use, only in case the regular signal circuitD should develop a fault, when signals could be transmitted temporarilyover the conversation circuit. and s of jack J are normallyin contact,but separate on the insertion of a plugin the jack; While the twoadditional contact springs s and s are normally out of contact, but areelectrically united by the insertion of a plug in the jack socket; theseconstitute circ'uit changers determining the condition of shuntcircuits.

The main station trunk circuit L extends from the local switchboard M tothe toll board T by the wires 8 and 9 which terminate respectively inthe springs 8 these being normally united through theiranvil contacts 2and the drop a. When the twin plug P is placed in the jacks J J thisnormal union is dissolved, and the said trunk conductors 8 and 9 areextended to the two members 135 and p of the other twin plug P Theinterstation trunk L enters the central station by conductors l0 and 12which are normally united through their contact springs 8 restingcontacts .2 the loop 44:, and the annunciator A WVhen the second twinplug P is inserted in this or any like pair of jacks, this normal unionis dissolved and the two conductors 10 and 12 of the toll line L areextended through the office trunk L to the terminal plug thereof P, andwhen the said plug P is insertedin the jack J of any line L, the saidline and the toll line, are united for thorough oral communication. Noportion of the conversation circuit so formed, has ordinarily anyelectrical The two additional contact springs 3 IIO relation to thesignaling circuit now to be described, although the plug P by itsremoval. from, or replacement in its resting socket or seat Smechanically actuates the circuit controller or closer Oof the signalcircuit D by uniting or severing its contact points 0 and 0 Thesignaling circuit irrespective of its route under any given conditionsterminates at the two ground connections G and G or such an equivalentreturn conductor as is indicated in the broken line R and necessarilyincludes the battery or other generator B, and the circuit closer O,which is held open by the handle of the plug P when in place, and whichis closed whenever the said plug is not in place. When the circuit isnot in operation, and the plugs at both ends are not in use, thesignaling circuit between the switchboards M and T is traceable asfollows: earth at G, wire 22, circuit closer O, the points 0 and 0 beingseparated, conductor 45, the self-setting annunciator S, conductor 46,low resistance coil H of the relay R, conductors 47 and 48, highresistance coil H of the relay R, and conductor 49 at the local board,over conductor 50 to the toll board, thence through the high resistancesignal annunciator A, and conductors 51, and a portion of 24 to one poleof the generator B, the other pole of which is earthed at G or as beforestated connected with the return conductor R It will be also observedthat a shunt circuit is provided around the high resistance coil H ofthe relay R, which shunt is closed by the normally established contactbetween the points 8 and s in springjack J at the toll board, the saidshunt circuit extending from the junction point a on one side, to thejunction point a on the other side of the relay coil H, by way ofconductor 52, jack contacts 8 and s and conductor 53. Under theseconditions therefore, the low and high resistance signal indicators Sand A and the low resistance relay coils H are all in the signalingcircuit D, which however is open at O, and the high resistance relaycoil is connected therewith, but short circuited by the shunt. If nowthe plug P be removed from its seat S the circuit closer 0 will operateand close the circuit of the generator B through the ten ohm signal S,the one hundred ohm signal A and the ten ohm coil H of the relay. Thesignal S will not operate because the current is too enfeebled by thepresence of the high resistance coils of A; the relay coil 1-1 will notattract its armature, because, partly for the same reason, and partlybecause it has in any case but a feeble magnetizing power, it does notsufficiently magnetize its core g to enable said core to attract thearmature q the relay coil H does not aid in mag netizing the said core,because it is shunted; but the one hundred ohm signal A at the tollboard having a large number of convolutions, is able todevelop aconsiderable magnetizing power, and does operate and give its signal,ordinarily by dropping a shutter. Thus the signal circuit having beenquiescent, can by the action of an operator at the local board M intaking up the trunk terminal plug to make a conversation circuitconnection, be automatically operated to give a signal at the tollboard, indicating that a connection with the office trunk L is desired,to which signal the toll board operator at once responds by insertingthe plug P into the trunk jacks J and J which action separates thespring points 8 s and also brings into contact the Spring points 5 and.9 thus opening the normal shunt round the relay coil H, and closing anindependent and normally open shunt round the high resistanceannunciatorA between the junction point a on one side, and the junctionpoint a on the other side thereof, by way of conductor 54:, point aspring contacts 3, and in jack J and conductor 55. When therefore theoffice trunk L is in use, the signal circuit D, is closed at O, and thecircuit includes the low resistance signal S at the board M, and bothcoils of the relay R; while the annunciator A at the toll board isshort-circuited by the closing of its shunt circuit at the points 3 s inthe jack J this signal A may thus be reset, and cannot again be actuateduntil the plug P be withdrawn from its jack. In fact the shunt throughthe contacts in jack J 4 only becomes necessary to allow that operation.It could be dispensed with by using a self-setting annunciator similarto that marked S, but of the high resistance required. Under theseconditions, the signal S still remains inoperative, because theresistance of the circuit being unchanged by the mere substitution ofthe one hundred ohm relay coil for the one hundred ohm slgnal A, thecurrent in the circuit is no stronger than at first, and is too feebleto operate said signal with the said high resistance relay coil also incircuit. But the relay having both coils in circuit becomesoperative,thenumerousconvolutions of its coil H compensating for the weakness ofthe current; the armature g is attracted, and the relay points g beingbrought into contact, asecond or supplementaryshunt circuit, is thusclosed through said points round the resistance of the toll board signalA, between the two junction points a and a by the way of conductor 24,relay frame q,'armature (1 points g and wire 60; the said annunciator Abeing alreadyshunted between the two points a and a through the jackpoints 8 and 8 as before described. The battery current thus has nowtwolow resistance routes to the points a at which it enters the relay.These circuit conditions remain until the first motion tending to adisconnection is made. The only disconnecting or clearing outannunciator in the conversation circuit is the annunciator e in the linkconnection circuit at the toll board T. Therefore no matter which of thetwo connected substations sends the disconnecting signal, it is receivedat the toll board, and as a consequence the first motion ofdisconnection is inall cases ICC made there, and consists in thewithdrawal of the plugs 1 and P This action mechanicallyrecloses the shunt circuit around the high resistance relay coil 'by reuniting thepoints 5 and s in the jack J and thereby reduces the magnetizing powerof said relay; but the armature is not retracted, nor are the points (1separated, because the magnetizing power of the low resistance relaycoil H though insuflicient to attract the armature, is quite sufficientto sustain said attraction; and the second shunt circuit around the tollboard annunciator A remains thus closed. The same action also opens thefirst shunt circuit round the said annunciator by permitting the points5 s in jack J once more to separate. The signal circuit D is nowrelieved from the resistance of the annunciator A, as well as thatof therelay coil 11 and consequently the coil H of the said relay is to someextent strengthened, and the current also becomes strengthened, sothat-it now excites the low resistance magnet of the signal S at thelocal board, which operates, displaying its signal, and indicating atthe local board M that a disconnection has been initiated at the tollboard I, by the withdrawal of the plug P The purpose of the signal S isto notify the local board operator to complete the disconnection bywithdrawing in turn the plug P from its jack, and replacing the same inits seat S and until this is done the visual signal S will continue itsdisplay. It is however a self-restoring or selfsetting indicator, and assoon as the plug is restored to its seat, and the circuit controller isthereby operated, the current thus being withdrawn from the signalingcircuit, the said signal S is displayed no longer and disappears. Theorder in which these operations have taken placeis that which isfollowed when the connection is called for by some substation connectedwith the home switch-board. Such an order reaches the operator at thesection M thereof, by means of the instruction circuit L connected withhis telephone t and leading from other sections. The same operationstake place when the connection is intimated by some station outside, andto be reached over some circuit L, in which case the toll board Tcommunicates with the operator at the local board M by touching the endsof the twin plug P to the terminal plates 0' of the instruction circuitL leadingto theoperators telephone t although the order of theoperations would be different. In the first case the toll board operatoris apprised that a connection is desired by the operation of the drop Aconsequent upon the removal of the plug P from its seat, and connectinghis plug to the jack J 3 associated with such drop, he answers thesubstation which has been connected at M with the trunk L and finds whatstation is wanted. In the second case, the toll board communicatesorally with the operator at M as described, and states the number of thelocal substation wanted, and the trunk to be used, whereupon theoperator at M inserts the plug end of said trunk in the jack of thatnumberif the wanted line be not already busy, and leaves it so, untilthe display of the signal S indicates the conclusion of the message. Butif the line be busy, the operator places the plug P in the busy jack Jand this operates the clearing out drop 6 at the toll board, indicatingthat the connection desired cannot for the present be had. It thusappears that though the signal circuit is quite distinct from thetalking circuit, no connection or disconnection can be made with eitherterminal of the office trunk forming part of such talking circuitwithout in some way affecting the said signal circuit. The signalcircuit has a shunt circuit for thehigh resistance relay coil normallyclosed, but opened by the insertion of the plug at the toll board; andtwo shunt circuits for the toll board annunciatorA,both normally open,one of which is closed whenever the plug P is placed in its jackregardless of other conditions, while the other can only be closed whenthe plug is placed in its jack at the same time the local board plug Pis removed from its resting place, but once closed remains so until theplug P is replaced in its seat, even though the plug P be withdrawn. Theobject of this is to provide that the signal S once displayed willcontinue in sight and to display itself until the plug P shall have beenwithdrawn from any jack in which it has been used, and that beingdependent upon such withdrawal, it shall immediately thereupon displayitself no longer.

The entire series of signaling operations may be summed up as follows:

First. Then the plug P is taken from its seat S the visual self settingsignal S does notwork because it is in series with both the lowresistance relay coil, and the high resistance signal A at the tollboard. The relay does not work because its high resistance coil isshunted through the points .9 s in the jack J while its low resistancecoil is in series with the signals S and A; but the signal A does work,and gives its signal at the toll board.

Second. When the plug P is removed from its seat S the twin plug at thetoll board having previously been inserted in its jack, the visual selfsetting signal S does not operate because it is now in series with bothrelay coils. The relay does work because its high resistance coil isincluded in the direct circuit of the battery; and the high resistanceannuncia-tor A at the toll board does not work, because it is shunted orshort circuited through the jack points 5 8 Third. When, (the plug P,being removed from its seat or socket S the plug at the toll board hasbeen inserted in its jack and is now withdrawn, the visual self-settingsignal S (the appearance of which always instructs the operator that theplug P should be replaced in its socket) is operated, because the onlyresistance now in series with it is the low resistance relay coil. Therelay remains in operation, because its low resistance coil has only thesignal Sin series with it, and

' thus has quite sufficient magnetizing power to maintain the attractionof its armature. The high resistance relay coil and the high resistancecoil of the toll board annunciator A are neither excited because theyare both short circuited; the former through the jack points, the latterthrough the relay points. The function of the relay is therefore tomaintain the resistance of the circuit sufficiently low to permit theoperation of the signal S by establishing a temporary shunt around thesignal A which shall automatically be broken as soon as the object ofthe said signal S is achieved and the plug P restored to its position ofrest.

'We have throughout this specification so far referred to the use oftwin jacks J and J and twin plugs P at the toll board end of the localtrunk L But double main conductor jacks, and double conductor plugs,such as the loop plug shown in connection with switchboard M, in whichone conductor terminates in the tip and the other with the sleeve of theplug are well recognized as being equivalent devices and we may, andfrequently do substitute them at the toll board for the twin form ofappliance. In like manner we may use two single plugs instead of thetwin plug, if we so elect. Furthermore it is evident that instead ofplacing the circuit closing contacts of the signaling circuit D in theresting socket of the plug P, we may place them in the jack J andconnect and disconnect them by the insertion or withdrawal of the plug.

Having now fully described our invention, we claim- 1. The combinationof an electric circuit; a plug connector constituting a movable terminaltherefor; and a resting socket or seat for the said plug; with a key orcircuit changer having a spindle capable of vertical movement in onedirection when pressed, and in the opposite direction under theinfluence of a spring, in juxtaposition to the said resting socket; anda retaining device adapted to engage the said key when depressed duringthe absence of the said plug from its socket, and to maintain saiddepression; but to release the same upon the replacement of said plug,substantially as described.

2. The combination of a telephone circuit; a plug connector constitutinga movable terminal or connection thereof and a resting socket therefor;an induction coil; and a circuit changing key controlling the connectionof said induct-ion coil with said circuit, associated with and mountednear to said resting socket; with a controlling spring for the said keydepending for its position upon the presence or absence of said plug inits resting socket, and capable of engaging the said key if depressed toconnect the induction coil, when the plugis absent from the said restingsocket, but adapted to release the same and to cause the automaticdisconnection of the said induction coil upon the replacement of saidplug in said resting socket, substantially as described.

8. The combination of an electric circuit; a repeating induction coiladapted for inclusion therein; a press key or circuit changercontrolling the connections of said coil with said circuit, the said keyhaving a shouldered shank and adapted to move vertically in onedirection when manipulated, and reversely by means of a spring; with aplug connector; a normal seat or resting socket therefor; a controllingspring for the said key fixed at one end, having a perforationencirclingthe shank of said key and adapted thereby to engage theshoulder thereof, and maintain the connection of the induction coil withthe circuit; and a mechanical spring connection between the said plugseat and said controlling spring whereby the latter may be permitted toengage the key when the plug is absent from said plug seat, but iscaused to release the said key on the replacement thereof,substantiallyas described.

4. The combination with an electrical circuit; and a plug connectortherefor normally resting in a suitable socket or seat; of a repeatinginduction coil, adapted to be manually included in and automaticallywithdrawn from such circuit; a vertically moving key controlling theinduction coil circuit connections, and adapted when depressed to con-'nect the said coil with said circuit, and when retracted to withdraw thesame therefrom; a retaining device for the said key adapted to engagethe same and to maintain the depression thereof; and controllingmechanism for the said retaining device itself controlled by the removalfrom and replacement in its resting socket of the said plug, and adaptedon said replacement to free the said key from the said retaining device;substantially as described.

5. A normally open signaling circuit comrisin a main section includin anelectrical i P s a:

generator, a relay having independent high and low resistance helices, arelatively high resistance annunciator; a relatively low resistance selfsetting annunciator, and an automatic main section circuit closer;combined with a shunt circuit round the high resistance relay coil,normally closed through separable contacts in one of a pair of twinspringjacks; an independent shunt circuit round the high resistanceannunciator normally open between contacts in the remaining twinspringjack; a twin plug for the said springjacks adapted when insertedto close the said annunciator shunt, and open the said relay shunt; anda supplementary normally open shunt round the said annunciatorcontrolled by the said relay, and arranged to be closed thereby for thepurpose of reducing'the resistance of the main circuit, and of operatingthe said low resistance annunciator on the withdrawal of the twin plugs,substantially as described.

6. The combination with a trunk telephone line between two switchboardshaving a plug terminal in a resting socket at one, and springjack andplug connections at the other of said boards; with an independentassociated signaling circuit, having at the plug terminal switchboard aself setting annunciator responsive (when the said plug terminal isremoved from its socket) to the withdrawal of the plug from its jack atthe other switchboard; and having at the said other switchboard anannunciator responsive to the removal of the trunk terminal plug fromits said resting socket; substantially as described.

7. The combination with a terminal connecting plug at one end of atrunktelephone circuit; a terminal twin springjack and twin plugs therefor atthe other end of said circuit; of an associated signaling circuit havinga circuit controller actuated by the removal and replacement of saidterminal plug from its resting socket, and operating to close and opensaid signaling circuit; a circuit changer in each of the said twinspringjacks operated by the insertion and withdrawal of the twin plugsthereof to close and open shunt circuits of the said signaling circuits;arelatively high resistance annu nciator normally in the signalingcircuit at the twin springjack end of the telephone circuit, and adaptedto give its signal when the said signaling circuit is closed by theremoval of said terminal plug; means for short circuiting or shuntingthe said annunciator when the said twin plug is inserted in the saidtwin springjacks, and for maintaining the said short circuit on thewithdrawal of said twin plug, until the said signaling circuit is brokenby the replacement of the terminal plug; and a relatively low resistanceindicator in the said signaling circuit at the terminal plug end thereofadapted to give its signal only when the circuit having first beenclosed by the absence of the terminal plug from its resting socket, thehigh resistance annunciator is short circuited by the insertion andwithdrawal of the said twin plug, and to restore its signal when thesignaling circuit is opened by the subsequent replacement of the saidterminal plug, sub stantially, as described.

8. The combination with a trunk telephone line between two switchboardsfitted at one of said switchhoards with twin springjacks adapted toreceive a twin. plug, and at the other with a terminal cord and plughaving a suitable plug seat or resting socket; of an associated normallyopen signal circuit and apparatus independent thereof, comprising thefollowing elements, a circuit closer mounted in the said plug seatactuated by the removal and replacement of said plug to close and reopenthe signaling circuit; circuit changers mounted within the said twinspringjacks at the other end of signaling circuit, actuated by theinsertion and withdrawal of the twin plugs to establish and disestablishshunt circuits, and thereby vary the resistance of the main circuit; anannunciator normallyin the signaling circuit at the springj ack end ofsaid trunk organized to respond to the closure thereof by the removal ofthe said terminal plug from its socket; arelay normally sh unted fromthe signaling circuitbut included therein by the operation of one of thesaid springjack circuit changers; a shunt circuit round the saidannunciator closed by the operation of said relay; and a self settingannunciator at the plug end of said trunk, organized to respond onlywhen the signaling circuit is closed by the removal of the terminal plugand when its resistance is reduced by the establishment of shuntcircuits round the said annunciator by said relay, and round said relayby the withdrawal of said twin plug substantially as described.

0. The combination with an office trunk line extending between a localand a toll switchboard and provided at the former with a terminal plugand a resting socket therefor, and at the latter with twin terminalspringjacks adapted to receive twin connecting plugs; of an automaticsignaling system of circuits comprising a normally open main section; abattery therefor;a circuit controller placed in the resting socket ofsaid plug, and operated by the removal and replacement thereof; anannunciator at the toll switchboard in said main circuit responsive tothe withdrawal of said plug; a relay having independent high and lowresistance coils or helices; a shunt circuit round the high resistancecoil of said relay normally closed through contact points in one of saidtwin springjacks, but adapted to be opened on the insertion of the plugtherein; an independent shunt circuit round the toll board annunciatornormally open between contact points in the other of said twin jacks,and adapted to be closed by the insertion of the plug; a second normallyopen shunt circuit round the said annunciator controlled by the saidrelay; and a self setting indicator at the local board responsive to thewithdrawal of the twin plugs at the toll board, only when shunt circuitsare closed round the high resistance relaycoil, and the toll boardannunciator, and when the terminal plug at the local board is absentfrom its socket and resetting itself on the replacement of said plug,substantially as described.

10. The combination withatrunk telephone circuit between twoswitchboards terminating at one of said switchboards in a cord and plug,and a resting socket for said plug when not in use; of a normally openassociated signaling circuit, including a battery; an automatic circuitcloser therefor mounted in the said resting socket, and actuated by theremoval of the said plug therefrom, and an ann un ciator in saidsignaling circuit at the other switchboard adapted to give its signalwhen the said circuit is closed, and thereby to respond to the removalof said plug from said socket, substantially as described.

11. The combination with a trunk telephone circuit extending between twoswitchboards, terminating at one of said switchboards in a cord andplug, and at the other in a twin or loop springjack, and having aresting socket for said plug, and a twin or loop plug for saidspringjacks; of a normally open associated signaling circuit including abattery; an automatic circuit closer therefor mounted in said restingsocket and actuated by the removal and replacement of said plug; a highresistance relay and annunciator connected with said signaling circuit;a low resistance annunciator capable of giving its signal on the closureof the circuit only after said high resistance has been shunted; acircuit changer in the said springjack shunting the said relay, and asupplementary shunt controlled by the said relay for the said highresistance annunciator; whereby the said low resistance annunciator maybe operated and caused to give its signal when the terminal plug is notin its socket by the insertion in and withdrawal from its springjack ofthe said twin or loop plug, and whereby the said signal may be withdrawnby the replacement of said plug in its resting socket; substantially asdescribed.

12. The combination with a telephone circuit extending between twopoints terminating at one of said points in a cord and plug; of anormally open associated signaling circuitincluding an electricalgenerator; an automatic circuit closer therefor actuated by connectionsand disconnections made by said terminal plug; and an annunciator insaid signaling circuit at the other of said points, adapted to give itssignal when its circuit is closed by the act of making a connection withsaid plug; substantially as described.

13. The combination, substantially as hereinbefore described with atelephone circuit, extending between two switchboards, and terminatingat one of them in an extensible cord and plug; of a normally openassociated signaling circuit including an electrical generator; anautomatic circuit closer therefor actuated by the operation of saidplug; two annunciators in the signaling circuit, the first responsive tothe operation of said circuit closer directly and the second to theoperation of said circuit closer, only when the first is shunted.

In testimony whereof we have signed our names to this specification, inthe presence of two subscribing witnesses, this th day of December,1892.

FRANK A. PIOKERNELL. FRANCIS W. DUNBAR. Witnesses:

CHARLES D. M. COLE, R. J. MORGAN.

